Effects of Microstructures and Porosity on Tensile Properties of Al-Si-Cu Cast Alloys

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  • Al-Si-Cu系鋳造合金の引張特性に及ぼすミクロ組織及びポロシティの影響
  • Al Si Cuケイ チュウゾウ ゴウキン ノ ヒッパリ トクセイ ニ オヨボ

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Abstract

  The effects of microstructure and porosity were investigated on the tensile properties of AC4B type Al-Si-Cu cast alloys containing 7 mass % Si, 3 mass % Cu, 0.17 mass % Mg, 0 to 0.72 mass % Fe and 0 to 0.4 mass % Sr. The specimens were solidified at a cooling velocity of 2.7 K/s or 14.4 K/s in metallic molds. T6 heat treatment was applied to a group of specimens. Since the crack generates from porosity, iron-rich compound and eutectic Si particle, the relation of the tensile properties and the size and morphology of the defects was investigated. Porosities larger than each crystallized phase appeared in the specimens cooled at 14.4 K/s, though the melt was degassed by bubbling a dry Ar gas through it. The crack initiated from larger porosities in the tensile test. In particular, the elongation decreased with the increase in the maximum size of the porosity. On the other hand, larger acicular or Chinese script type iron-rich compounds developed in specimens cooled at 2.7 K/s. The compounds lowered both the tensile strength and elongation, though they tended to raise the 0.2 % proof strength. Higher cooling velocities and proper amounts of Sr addition refined the microstructure and porosities, hence improving the tensile properties of both the as cast and T6 specimens.

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